Indicate the level of significance in an R xtable

Question

In a regression analysis R "rates" each independent variable with its level of significance (i.e. with stars **), e.g.:

Coefficients:
            Estimate Std. Error t value Pr(>|t|)    
(Intercept)   7.0869     0.6504  10.897  < 2e-16 *
X1          -2.1953     0.3160  -6.948 8.89e-12 ***
X2           0.2586     0.0778   3.324 0.000936 **
X3          -0.3415     0.1003  -3.406 0.000700 **
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 

But when you convert into Latex with xtable, the new table looks nice, but doesn't have the column with stars. How can I make xtable to include a column with the stars? Or else, how can I make that each row is colored to reflect the level of significance? Thanks!